1. Field of the Invention
This invention relates to sewing machines having a means for interchangeably using a cassette containing a supply of thread or a spool of thread for the thread supply.
2. Description of the Prior Art
Most sewing machines have heretofore been supplied with thread from a spool carried on the arm of the sewing machine. Sewing machines employing thread supplied from conventional spools are frequently difficult or confusing to thread due to the complexity of the path that must be followed to insure that the thread is engaged into the requisite thread handling instrumentalities in the proper order. While contemporary sewing machines have become increasingly easy to operate, there still remains the problem of accurate threading to insure precise stitch formation. The problem becomes even more acute when thread must be changed frequently to accommodate a new color or thread type demanded by a particular sewing situation.
One problem with prior threading systems is that they did not allow the interchangeable use of a cassette containing a supply of thread, or a spool of thread to supply the thread demands of the needle.
Another problem is that prior known thread cassettes were excessively complicated, thus contributing to prohibitive manufacturing costs.
Still another problem is that some prior known sewing machines adapted for thread cassette operation would not operate successfully unless the main shaft was rotated to a predetermined position prior to insertion of the cassette.